The need for efficient energy usage is ever-increasing. Many advances have been made, in the last few decades, to provide more efficient conversion of the potential energy of fuel to useful mechanical energy. A strong focus has been placed on the conservation of energy to ensure that future generations have sufficient, reliable energy sources. Even with this focus, staggering amounts of energy are still lost daily from industrial smokestacks, combustion engine exhausts, and from us simply passing by the opportunities available to make the most of naturally available and renewable energy sources. A key component of efficient energy usage is the recovery of energy from waste heat sources. Developments must be made to reclaim energy wasted in our daily processes and to utilize readily available and non-polluting energy resources.
The internal combustion engine (ICE), with reciprocating pistons, is probably the most widely known device used to convert potential fuel energy to mechanical energy. This type engine is much more efficient and versatile today than it was just a few decades ago. It is capable of using a slightly wider variety of fuels than in the past. This type of engine, in vehicles, may be configured with an electric motor to provide a more efficient hybrid.
One problem with the internal combustion engine, with reciprocating pistons, is residence time of the ignited fuel in the power-producing zone. The burning fuel exits the engine in a state of incomplete combustion. The full amount of the potential energy of the fuel cannot be imparted upon the pistons of the engine. Downstream equipment is required to fully combust the fuel before it exits to the atmosphere.
Another group of internal combustion engines, that is not as widely known, includes orbital, round, and toroidal designs. Some engines of these designs are capable of providing a longer residence time for the ignited fuel, however, they still fall subject to the same problem as the internal combustion engine with reciprocating pistons. The residence time of the fuel is limited. This type of engine is also limited in the variety of fuels it can use.
The current use of ICE-electric hybrid systems, and totally electric systems (an electric motor and rechargeable battery banks), to provide mechanical energy, is a seemingly credible effort toward more efficient fuel usage and more environmentally friendly methods. However, much of the electric power used by these systems originates from fossil fuels. Also, the batteries, required to store and release electrical energy in these systems, create their own environmental problems.
Another problem with many of the previously mentioned designs is their lack of process flexibility. These designs would require significant modifications if they were to be used for the purpose of waste heat recovery.